U.S. Pat. No. 4,137,845 discloses a printing unit in a multi-unit printing press. The printing unit includes a plate cylinder carrying a printing plate upon which an inked image is defined, and a blanket cylinder carrying a printing blanket which transfers the inked image from the printing plate to material being printed. The printing press includes a mechanism for adjusting the plate cylinder circumferentially, and also includes a mechanism for adjusting the plate cylinder axially. The mechanisms enable the circumferential and axial adjustments to be made independently of each other during the making ready of the printing press before printing is performed. The adjustments are made at the printing unit during the making ready of the multi-unit press so that the image printed by the printing unit will have precise registration with another image that is printed in an adjacent printing unit in the multi-unit press.
U.S. Pat. No. 4,953,461 discloses a printing unit having a mechanism for adjusting the position of the plate cylinder relative to the blanket cylinder during a printing operation, i.e., after the register settings have been made during the making ready of the multi-unit printing press. When the plate cylinder and the blanket cylinder are being rotated to transfer the inked image to the printed material, the mechanism disclosed in the '461 patent further rotates the plate cylinder relative to the blanket cylinder to change the surface speed of the printing plate relative to the surface speed of the printing blanket. The surface of the printing plate and the surface of the printing blanket therefore slide relative to each other in the circumferential direction during printing. The sliding movement of the two surfaces relative to each other reduces the amount of ink which tends to build up on the surface of the printing blanket.